DEPENDENCES OF THE INFLUENCE OF OVERHEATING TEMPERATURE ON CRYSTAL GENERATION IN METAL MELTS

Procesi littâ, 2023, Vol 3 (153), 34-40

Abstract

The work is devoted to establishing the regularities of the influence of the temperature of overheating of metal melts on supercooling, during which crystals nucleate in them, which determines the relevance of such scientific research. Due to the opacity of metals, which does not allow to visually trace the nucleation and growth of crystals in the process of forming cast blanks from them, this task was solved, in particular, by visual observation of the studied processes by the method of physical modeling on transparent organic media. For conducting research, a physical modeling technique was developed and a special experimental setup was created. When conducting research, a test tube with a model medium was placed in a thermostatically controlled chamber using a cassette. A transparent heat carrier (water or alcohol) was fed into the chamber from the thermostat, the temperature of which was gradually raised to a given level (in this way, the overheating temperature of the model melt changed). After the appropriate exposure of the melt in an overheated state, its cooling began at a certain speed by cooling the heat carrier in the thermostat with the help of a refrigerating unit. In experiments with a transparent model medium (commercial salol), visual observation of processes occurring in the melt (nucleation of crystals) was carried out through transparent faces. If necessary, for greater visibility of the observed processes, the camera was illuminated by a beam from a lamp through transparent faces, and the observed processes were recorded using a photo (video) camera. When the model medium was opaque (technical gallium), in order to fix the temperature of the beginning of the crystallization process, a thermocouple was lowered into the tube with the test sample, the signal from which was displayed on the laptop screen in the form of a temperature cooling curve. According to the characteristic changes in the temperature curve of the cooling of the model environment (due to the release of the heat of crystallization), the
amount of supercooling of the melt, at which the nucleation of crystals occurs, was determined. In the course of the conducted research, it was found that the influence of overheating on hypocooling of model environments is caused by the temperature dependence of the homogeneity of the tested melts due to the uneven distribution of the available soluble impurities. If we transfer the results of physical modeling to real objects, the influence of the temperature of overheating of metal melts on the subcooling, in which the nucleation of crystals occurs, is most likely caused by a change in their physical and chemical properties due to the dissolution of impurities.